Patterned light emitting diode devices

ABSTRACT

An LED device that emits light in a pattern is disclosed. The LED device is a layer of active material that is sandwiched between a transparent substrate with an anode formed thereon and a cathode. The active material has a layer of light emitting material that emits light when electron/hole recombination is induced in the material.  
     The patterned emission is defined by a patterned layer in the active material of the LED device. The patterned layer has at least a first thickness and a second thickness. When the device is on, the portion of the device associated with the first thickness of the patterned layer is visually distinct from the portion of the device that is associated with the second thickness of the patterned layer.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The invention is directed to Light Emitting Diodes (LEDs) and, inparticular, to LEDs that emit light in a pattern.

[0003] 2. Art Background

[0004] Flat panel displays containing light emitting diodes areubiquitous features of many products. Because of the need to minimizethe manufacturing cost of most products, inexpensive ways to manufactureflat panel displays are of considerable interest. As noted in Lidzey, D.G., et al., “Photoprocessed and micropatterned conjugated polymer LEDs,”Synthetic Metals, Vol. 82, pp. 141-148 (1996), organic materials havebeen investigated for use as the emissive layers in LEDs becauselarge-area devices can be made cheaply and easily using such materials.Also, a greater variety of emission colors is obtained when organicemissive layers are used instead of inorganic emissive layers. LEDs withorganic emissive layers have a greater electrical efficiency thancomparable LEDs with an inorganic emissive layer.

[0005] LEDs are generally formed on transparent substrates such as glassor plastic. A light emitting material is sandwiched between an anodeformed on the substrate and a cathode. When current is supplied to theanode, electrons and holes recombine in the light-emitting materialsandwiched between the anode and the cathode. As a result of thisrecombination, light emits from the light-emitting material and throughthe transparent substrate.

[0006] One use for LEDs is in displays having a fixed pattern. In suchdisplays, there are at least two areas of contrast when the display ison. The areas of contrast (e.g. light and dark) provide a desiredpicture (e.g., a logo) or message (e.g. an “EXIT” sign). Such apatterned array of LEDs is described in the previously mentioned Lidzeyet al. reference which was mentioned previously. A patterned cathode isformed over an emissive layer (poly(2,5-dialkoxy-p-phenylenevinylene).When a voltage is applied to the ITO anode, light is emitted in apattern that corresponds to the cathode pattern, because light is onlyemitted from those portions of the emissive layer sandwiched between theanode and the cathode. A patterned display is also obtained bypatterning the anode instead of the cathode.

[0007] However, there are certain limitations on the patterns that canbe obtained by patterning the anode or the cathode. For example, asimple pattern such as the letter “O” is not easily obtained bypatterning the cathode. This is because the mask used to form thepattern must be one integral unit. The letter “O” requires completephysical separation between the portion of the mask inside the “O” fromthe portion outside the “O.” Such a complete physical separation cannotbe obtained in a single unit mask. There must be some physicalconnection between the portion of the mask inside the “O” and theportion of the mask outside the “O.” Furthermore, the expedients used topattern the cathode in the manner described in Lidzey et al. degrade theorganic emissive layer underlying the cathode.

[0008] Different restrictions are placed on a patterned anode such asindium tin oxide. For example, the conductivity of ITO is reduced whenpatterned into narrow lines. Therefore, the brightness of the display isnot evenly distributed if a narrow portion of ITO is required by thepattern. Furthermore, the ITO must be electrically interconnected andtherefore a pattern that is not continuous is not practicable.

[0009] In response to the limitations imposed by patterning anodes andcathodes, Renak, M., et al., Microlithographic Process for PatterningConjugated Emissive Polymers,” Advanced Materials, Vol. 9, No. 5, pp.392-395 (1995) describes a patterned LED display in which the electronemissive layer (poly(p-phenylenevinylene)) is patterned. Renak et al.describes a device in which the patterned layer ofpoly(p-phenylenevinylene) (PPV) is formed over an ITO layer. An electrontransport layer was cast over the PPV layer. A cathode was formed overthe electron transport layer. The electron transport layer is present toprevent direct electrical contact between the ITO anode and the cathode.

[0010] When a voltage is applied to the ITO of the device described inRenak et al., light is emitted from the patterned PPV layer in thepattern of the PPV layer. However, the approach does not afford muchflexibility, as the only contrast provided by such a display is thecontrast between the PPV area of the display (which emits light when thedevice is on) and the non-PPV area of the display (which does not emitlight even when the device is on). Thus the basis for contrast in such adisplay is basically either on or off. Furthermore, Renak et al requiresthe use of light-emitting polymers that are also photosensitive in orderto pattern the light-emitting layer. Thus, the choices for thelight-emitting material for the Renak et al. device are extremelylimited.

[0011] A display that provides the potential for a greater variety ofvisual contrast, yet does not require that either the anode or thecathode be patterned, is desired.

SUMMARY OF THE INVENTION

[0012] LED devices have a layer or layers of active material sandwichedbetween an anode and a cathode. Active layers, as used herein are layersof material in which either electron transport, hole transport, lightemission, or some combination thereof, occur. The present invention isdirected to an LED device in which at least one of the active layers ispatterned to have at least a first thickness and a second thickness. Thepatterned organic layer is sandwiched between an anode and a cathode.When the LED device is on (i.e. when sufficient current is provided tothe anode to induce electron/hole recombination in the light emittinglayer) there is a visually perceivable contrast between the portion ofthe LED device that corresponds to the active layer of the firstthickness and the portion of the LED device that corresponds to theactive layer having the second thickness.

[0013] The active layer is one or more layers of organic material. Inone embodiment, the active layer is a patterned layer of a material inwhich electron/hole recombination and, thus, light emission occurs. In asecond embodiment, the active layer is a combination of two layers: alayer of material in which light emission occurs coupled with a holetransport or electron transport layer. The hole transport layer, ifpresent, is in contact with the anode. The electron transport layer, ifpresent, is in contact with the cathode. In the second embodiment, theaggregate thickness of the active layer (i.e. the combined thickness ofthe light emitting layer and the hole transport or electron transportlayer) is not uniform because one of either the light emitting layer andthe electron transport layer or the hole transport layer is patterned.An active layer consisting of a patterned electron transport layerformed on a layer of light emitting material of uniform thickness is oneexample.

[0014] In a third embodiment both the light emitting layer and the holetransport or electron transport layer are patterned. However, thepatterns are complimentary (the thinner portion of one layer is alignedwith the thicker portion of the other layer and vice-versa) so that theaggregate thickness of the two layers is uniform.

[0015] As a result of the one or more patterned layers in the activelayer, the LED device emits light through one portion associated with afirst layer thickness that is visually distinct from a second portion ofthe LED device associated with a second layer thickness. In the contextof the present invention, the thickness that is referred to is thethickness of the patterned layer and not the aggregate thickness of theactive layers. In one embodiment of the present invention, when the LEDis on, the LED device only emits light through the portion associatedwith the thinner portion of the patterned light-emitting layer and notthrough the second portion associated with the thicker portion of thelight-emitting layer. In an alternate embodiment, the LED device emitslight of a first color through the first portion and light of a secondcolor through the second portion. In yet another embodiment, the LEDdevice emits light of a first intensity through the first portion andlight of a second intensity through the second portion. In thisembodiment, the difference between the first intensity and the secondintensity is visually perceivable.

[0016] It is also contemplated that the patterned layer has more thantwo thicknesses. When the LED device is on, the region of the LED deviceassociated with a particular thickness of the patterned layer isvisually distinct from the other regions associated with the otherthicknesses. The LED device of the present invention provides theflexibility to produce LED devices in a variety of patterns. The LEDdevices of the present invention are produced at low cost because of theease in which a patterned layer is formed.

[0017] Since the light-emitting material of the LED of the presentinvention is sandwiched between an anode and a cathode, one of eitherthe anode or the cathode is transparent to the emitted light so that thelight emission is observable. Typically one of either the anode or thecathode is formed on a substrate. If the transparent anode is formed ona substrate, then the substrate on which the anode is formed is alsotransparent. Similarly, if the transparent cathode is formed on asubstrate, then the substrate on which the cathode is formed is alsotransparent. For convenience, in the embodiments described herein, theanode is formed on the substrate. However, the present inventioncontemplates that the patterned active layer of the device of thepresent invention can also be placed between a cathode formed on asubstrate and an anode. Furthermore, in certain embodiments the anode orthe cathode is the substrate.

[0018] In one embodiment of the present invention, the LED device isformed by spinning a precursor of the organic light emitting material ona transparent substrate with an anode formed thereon. It is advantageousif the precursor is soluble in an organic solvent such as methanol. Amold is used to form the layer of precursor into a desired pattern. Anelastomeric mold that has a first surface with a recessed portion in thedesired pattern is one example of a suitable mold. The recessed portionfunctions as a channel for the precursor when the mold surface is placedin contact with the layer of organic light emitting material.

[0019] The mold surface is wetted with an organic solvent. When thewetted surface contacts the precursor, the precursor is partiallydissolved and the dissolved precursor fills the channels in the mold.The solvent is evaporated and the mold is removed. After the mold isremoved, the precursor layer has a surface relief pattern thatcorresponds to the pattern in the mold. In order to form a lightemitting layer with three or more thicknesses, a mold that has channelswith more than one depth is contemplated as suitable.

[0020] In the context of the present invention, any light emittingmaterial that can be formed on a substrate in a desired pattern iscontemplated as suitable. A precursor of poly(p-phenylene vinylene) isone example of a suitable material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The advantages, nature and various additional features of theinvention will appear more fully upon consideration of the illustrativeembodiments now to be described in detail. In the accompanying drawings:

[0022]FIG. 1 is a schematic side view of an LED device of the presentinvention;

[0023]FIG. 2 is a perspective view of a relief pattern used to form amold which is then used to form a patterned layer of light-emittingmaterial.

[0024]FIG. 3 is a perspective view of an elastomeric material in contactwith the relief pattern of FIG. 2.

[0025]FIG. 4 is a perspective view of a mold in contact with a layer oflight-emitting material.

[0026]FIG. 5 is a perspective view of a layer of light-emitting materialwith a relief pattern formed therein.

[0027]FIG. 6 is a top view of a patterned LED device of the presentinvention in its on state.

[0028]FIG. 7A is a schematic side view of a second embodiment of an LEDof the present invention.

[0029]FIG. 7B is a top view of the device of FIG. 7A in its on state.

DETAILED DESCRIPTION

[0030] The present invention is directed to an LED device that has anactive layer that is sandwiched between an anode and a cathode. Theactive layer at least contains a layer of light emitting material, andoptionally contains either an electron transport layer, a hole transportlayer, or both. At least one of the light emitting layer, electrontransport layer or hole transport layer has at least a first thicknessand a second thickness. When the LED device is on, a first portion ofthe LED device associated with the portion of the layer having the firstthickness is visually distinct from a second portion of the LED deviceassociated with the portion of the layer having the second thickness. Inone embodiment of the present invention, the first portion of the LEDemits light and the second portion does not emit light. In a secondembodiment of the present invention, the first portion emits light of afirst color and the second portion emits light of a second color. In athird embodiment of the present invention, the first portion emits lightof a first intensity and the second portion emits light of a secondintensity.

[0031] In an alternate embodiment of the present invention, there aremore than two portions of the LED device, each associated with adifferent layer thickness. Each portion is visually distinct from theother portions when the LED device is on (i.e. the first portion is off,the second portion is a first color, the third portion is a secondcolor, etc.).

[0032] One example of an LED device of the present invention isillustrated in FIG. 1. The LED device 10 is formed on a transparentsubstrate 15. Examples of suitable substrates include glass andtransparent plastic substrates. The use of plastic substrates is limitedbecause the substrate cannot be exposed to temperatures that exceed themelting point of the substrate during subsequent processing. However,plastic substrates are attractive alternatives when suitable becausethey are lightweight, inexpensive, and flexible, among other advantages.

[0033] An anode 20 is formed on the substrate 15. The anode is aconventional material such as indium tin oxide (ITO). A layer of a lightemitting material 25 is formed on the anode 20. The light emittingmaterial is an organic material such as poly(p-phenylene vinylene)(PPV). Organic light emitting materials are well known to one skilled inthe art.

[0034] The layer of light emitting material has two thicknesses 26 and27. The voltage required to induce light emission from an organic lightemitting films is dependent on film thickness. For example, a voltage of6 V must be supplied to the anode to induce light emission in an 80 nmthick PPV film. A voltage of 12 V must be supplied to the anode toinduce light emission in a 200 nm thick PPV film. Therefore, if, forexample, a PPV film has a first thickness of 80 nm and a secondthickness of 200 nm, the portion of the film that is 80 nm thick willemit light when 6 volts is applied to the anode. However, the portion ofthe film that is 200 nm thick will not emit light when 6 volts isapplied to the anode. In the LED device depicted in FIG. 1, the firstthickness 26 is selected so that, when the device is on, the lightemitting layer does not emit light. The second thickness 27 is chosen sothat, when the device is on, the light emitting layer emits light.

[0035] A cathode 30 is formed over the layer of light emitting material.Conventional cathode materials are well known to one skilled in the art.All of these cathode materials are contemplated as suitable. Examples ofsuitable cathode materials are calcium, magnesium and aluminum.

[0036] In the embodiment of the present invention wherein light isemitted through the cathode, the cathode is transparent. One example ofa transparent cathode is a layer of aluminum that is sufficiently thinso that light emitted by the organic light-emitting layer passes throughit. In this embodiment, the substrate is not transparent, nor is theanode required to be transparent.

[0037] The thickness of the light emitting layer is controlled toprovide an LED device that emits light in a desired pattern. In theembodiment of the present invention wherein light is emitted by thefirst portion of the LED device and not emitted by the second portion ofthe device, the light emitting layer is patterned so that the thinnerportion corresponds to the desired pattern and the thicker portioncorresponds to the inverse of the desired pattern. A number oftechniques for forming the layer of light emitting material with twothicknesses, the first thickness forming a desired pattern in the layerand the second thickness forming the inverse of that pattern, arecontemplated as suitable.

[0038] One example of a suitable technique involves the use of a mold.In this technique, a mold is formed by casting an elastomeric materialagainst a topographic patterned surface. The patterned surface is thedesired pattern to be formed in the light emitting layer. An example ofa topographic surface is illustrated in FIG. 2. The surface 100 hasraised portions 110 formed thereon. The raised portions are formed usedconventional lithographic techniques in which a layer ofenergy-definable material is formed on a planar substrate. A pattern isintroduced into the layer of energy-definable material by introducing animage of that pattern into the layer of energy-definable material. Thatimage is introduced by exposing the energy-definable material topatterned radiation. The radiation introduces a chemical contrastbetween the exposed and unexposed portions of the energy-definablematerial. The pattern is developed by exploiting the chemical contrastbetween the unexposed portion and the exposed portion of theenergy-definable material. That is, the portion of the energy-definablematerial that does not correspond to raised portion 110 in FIG. 2 isremoved from the substrate.

[0039] The height of the raised portions 110 corresponds to thedifference between the first thickness and the second thickness in thelight emitting layer. Referring to FIG. 3, a layer of a liquid precursorof an elastomeric material 200 is formed over topographic surface 110.The topographic surface forms an impression in the elastomeric materialprecursor 200. The elastomeric material 200 is solidified and separatedfrom the topographic surface 110.

[0040] Referring to FIG. 4, the solidified, elastomeric material 200with impressions 210 formed therein is placed in contact with an organiclight emitting material 215 formed on a substrate 220 with an anode 225(ITO) formed thereon. The light emitting material 215 has a viscositythat permits it to flow into the impressions 210, which serve ascapillary channels for the light emitting material 215. One way toinduce the light emitting material to flow into the impressions is toselect a material such as a precursor of poly(p-phenylene vinylene)which can be spin cast onto the ITO-coated substrate. Since theprecursor is soluble in organic solvent, the surface 216 of theelastomeric material is wetted with an organic solvent such as methanol.Bringing the precursor into contact with the solvent-coated elastomericmold partially dissolves the precursor and causes it to flow into thechannels.

[0041] After the precursor has been molded into the desired pattern, theelastomeric material is removed from contact with the light emittingmaterial. If a precursor of the light emitting material is used, thatprecursor is then converted to the light emitting material using therequisite expedient (e.g. heating). The resulting structure 300 isillustrated in FIG. 5. In FIG. 5 the layer of light emitting material215 is formed on the glass substrate 220 with the layer of ITO 225formed thereon. The layer of light emitting material 215 has the reliefpattern formed therein which consists of a pattern of raised portions310 with a desired orientation and thickness. The thickness of theraised portions 310 is selected so that light will not emit from theseportions of the layer 215 when the LED device is on. The thickness ofthe thinner portion 350 of layer 215 is selected so that light will emitfrom this portion of the layer when the LED device is on. The emissionpattern of the LED device formed from the structure illustrated in FIG.5 is illustrated in FIG. 6. The light portion 410 of the LED device 400corresponds to the pattern of the thinner portion of 350 of layer 215(FIG. 5) from which light does emit. The dark portion 420 of the LEDdevice 400 corresponds to the pattern of the thicker portion 310 oflayer 215 (FIG. 5).

EXAMPLE 1

[0042] Films of a precursor of poly(p-phenylene vinylene) synthesizedfrom p-xylenebis(tetrahydrothiophenium chloride) via the Wessling routewere spin cast onto an ITO-coated glass substrate. The precursor wasobtained from Lark Enterprises of Webster, Mass. The films was cast ontothe substrate at a speed of 500 to 1000 rpm for 45 seconds. Thethickness of the resulting films were between 50 nm and 150 nm.

[0043] An elastomeric mold having a series of impressions formed in onesurface thereof was used to mold the precursor films. The impressions inthe surface of the elastomeric mold had a width of about 2 μm to about15 μm and a depth of 300 nm. The impressions were introduced into thesurface of the elastomeric mold by forming the elastomeric material overa topographic surface. The raised portions of that surface formed theimpressions in the elastomeric material. The raised portions wereprepared by patterning a layer of energy sensitive material on asubstrate. Conventional lithographic techniques were used to pattern theenergy sensitive material.

[0044] The surface of the elastomeric mold was wetted with methanol. Thesurface of the elastomeric mold with the impressions therein was broughtinto contact with the PPV precursor. After the solvent was evaporated,the mold was removed from contact with the precursor. The precursor wasthen baked at a temperature of 260° C. in vacuum (about 10⁻⁶ Torr) forabout 10 hours. Atomic force microscopy confirmed that the baking stepdid not significantly alter the surface relief imparted by the mold. Adual layer cathode was formed over the topographic PPV layer by vacuumdeposition of a layer of calcium (40 nm thick) followed by a layer ofaluminum (200 nm thick).

[0045] Light was observed to emit from the thinner (about 100 nm thick)portion of the PPV film when at least about 8 volts was applied to theresulting device. At this voltage light did not emit from the thicker(about 400 nm thick) portion of the PPV film. The device was observed tohave an external quantum efficiency of about 10⁻³% photons/electron. Theefficiency could be improved by forming a layer of electron transportmaterial over the PPV layer, choosing polymers with greater efficiency,or doping the polymer with a dye.

[0046] In order to avoid a change in brightness at the portion of theLED device that corresponds to a change a thickness of the lightemitting film in the device, one skilled in the art will appreciate thata steep profile is advantageous. The more gradual the transition fromfirst thickness to second thickness in the light emitting filmthickness, the greater the blur between the light emission effect of thefirst thickness and the light emission effect of the second thickness.Such a steep profile is obtained by ensuring that the indentations inthe mold surface have the desired profile. The precision of theseindentations is in turn dependent upon the accuracy of the method usedto form the indentations. In the embodiment of the present inventionwherein the indentations are formed by casting an elastomeric film overa topographic surface, the lithographic technique employed to formtopographic surface must be sufficiently precise to form features withthe requisite profile.

[0047] In an alternate embodiment, two or more different organic lightemitting materials are used to form an LED device that emits light in adesired pattern. For example, a first material emits green light when afirst threshold voltage is applied to an LED device with the firstorganic light emitting material. A second material emits red light whena second threshold voltage is applied to an LED device with the secondmaterial. The threshold voltage is the voltage that is required forlight emission to occur. If a voltage that is less than the thresholdvoltage is applied to the device, no light emits from the organic lightemitting material.

[0048] An LED device that emits light in a desired pattern is formedusing such materials. An example of such a device is illustrated in FIG.7A. The LED device 500 has a light emitting layer 510 which issandwiched between a transparent substrate 505 with an anode 506 formedthereon and a cathode 507. The light emitting layer 510 has a firstcontinuous layer of the first material 515 that has a patterned layer ofthe second material 520 formed thereon. Referring to FIG. 7B, which is atop view of the device 500 in its on state, the portion of the LEDdevice 500 associated with the single layer of the first material is525. The portion of the LED device associated with the dual layer offirst material 515 and second material 520 is 530.

[0049] If the first threshold voltage is greater than the secondthreshold voltage, then if a voltage is applied to the device 500 thatis greater than the first threshold voltage but less than the secondthreshold voltage, portion 530 emits light and portion 525 does not. Ifa voltage is applied to the LED device that is greater than thethreshold voltages of both the first material and the second material,then portion 530 emits light in one color and portion 525 emits inanother color.

[0050] For example, a device which, when a certain threshold voltage isapplied, emits red from one portion and green from another portion ofthe device is prepared by forming a layer of PPV on an ITO coatedtransparent substrate. A 100 nm thick layer of PPV emits green lightwhen 8 volts are applied to an LED device with such a layer. A layer ofALQ (aluminum tris(8-hydroxyquinoline) is formed over the PPV layer.Since ALQ over PPV also emits green light, the ALQ layer is doped tochange the color of emission from green to a color that contrasts withthe green light emitted by the single layer of PPV. The color ofemission can be changed by doping the ALQ layer with a fluorescent dyesuch as 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran(DCM) or 5,10,15,20-tetraphenyl-21H,23H-porphine. The concentration ofdye in the ALQ layer is typically about 1 to about 5 weight percent. Insome instances even higher concentrations of dye are used.

[0051] The ALQ layer is patterned. The ALQ layer emits at a lowerthreshold voltage than the PPV layer. Therefore, when a voltage isapplied to the LED device that is greater than the threshold voltage ofthe doped ALQ layer but less than the threshold voltage of the PPVlayer, light emits from the device in the pattern defined by the dualALQ/PPV layer. No light emits from the pattern defined by the single PPVlayer. When a voltage is applied to the LED device that is greater thanthe threshold voltages of both layers, red or red orange light(depending upon the choice of dopants described above) emits from thedual layer of doped ALQ and PPV. Green light emits from the single layerof PPV.

[0052] The patterned ALQ layer is formed on the PPV layer by vacuumdeposition using a shadow mask or by printing a solution solublered-emitting material on the PPV in the desired pattern. Examples ofsuitable printing techniques include screen printing, inkjet printing orspraying. In one embodiment of the invention, a layer of undoped ALQ isformed over the patterned, doped layer of ALQ. In this embodiment, thereis only one threshold voltage for emission. When the LED device is on,red or red orange light (depending upon the choice of dopants describedabove) emits from the tri layer of undoped ALQ, doped ALQ and PPV. Greenlight emits from the dual layer of undoped ALQ and PPV.

[0053] In another embodiment of the present invention, the voltageapplied to the device is selected to have a particular effect. In thedevice of the present invention, the voltage is selected so that lightemits only from the portion of the patterned layer that transitions fromthe first thickness to the second thickness. Although applicants do notwish to be held to a particular theory, it is believed that theselective emission from the transition region is due to the steep slopeof the material as it transitions from the first thickness to the secondthickness. Light emits from this transition region at a voltage that isless than the voltage required for the first portion of the LED to emitlight preferentially over the second portion of the device. An LED inwhich light emits from ordered arrays of small sources is useful in avariety of applications that use patterned light such as near-fieldphotolithography, near-field microscopy, spectroscopy, and high densityoptical data storage.

[0054] It is to be understood that the above-described embodiments areillustrative of only a few of the many possible specific embodimentswhich can represent applications of the principles of the invention.Numerous and varied other arrangements can be readily devised inaccordance with these principles by those skilled in the art withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. An LED device comprising: a substrate; an anode;a cathode; and an active material sandwiched between the anode andcathode wherein the active material comprises at least one materiallayer and wherein the at least one material layer is a layer of organiclight-emitting material and wherein at least one layer of the activematerial is a patterned layer having a first thickness and a secondthickness and wherein the layer of organic light-emitting material andthe patterned layer are the same layer or different layers and whereinwhen a voltage that is sufficient to cause light to emit from at least aportion of the organic light-emitting material, a first portion of theLED device associated with the first thickness of the patterned layer isvisually distinct from a second portion of the LED device associatedwith the second thickness of the patterned layer.
 2. The LED device ofclaim 1 wherein the active material has a first material layer and asecond material layer and wherein the first material is a light-emittingmaterial with uniform thickness and the second material layer is amaterial selected from the group consisting of hole transport materialsand electron transport materials that is patterned to have a firstthickness and a second thickness.
 3. The LED device of claim 1 whereinthe active material has a first material layer and a second materiallayer and wherein the first material is a light-emitting material thatis patterned to have a first thickness and a second thickness and thesecond material is selected from the group consisting of hole transportmaterials and electron transport materials that is patterned to have afirst thickness and a second thickness.
 4. The LED of claim 1 whereinthe first portion of the LED emits light and the second portion does notemit light.
 5. The LED of claim 1 wherein the first portion of the LEDemits light of a first color and the second portion of the LED emitslight of a second color.
 6. The LED of claim 1 wherein the first portionof the LED emits light of a first intensity and the second portion ofthe LED emits light of a second intensity.
 7. The LED of claim 1 whereinthe LED emits light from boundaries between the first portion and thesecond portion.
 8. A process for fabricating a patterned LED devicecomprising: forming a layer of an active material over one of either ananode or a cathode; placing a mold in contact with the layer of activematerial, wherein the mold is a surface with a patterned recessedportion therein; causing the active material to flow into the recessedpattern thereby forming a layer of patterned active material with afirst portion having a first thickness and a second portion having asecond thickness, the portion having the second thickness correspondingto the pattern defined by the patterned recessed portion in the moldsurface; removing the mold from contact with the active material; andforming the other of an an anode or a cathode over the layer of activematerial such that the active material is between one anode and onecathode.
 9. The process of claim 7 wherein the first thickness of theactive layer is selected to provide a first area of the light emittingdiodes associated with the first thickness that is visually distinctfrom a second area of the light emitting diode.
 10. The process of claim9 wherein the patterned active material is selected from the groupconsisting of a light-emitting material, a hole transport material, anelectron transport material, and combinations thereof.
 11. The processof claim 10 wherein the anode is formed on a substrate.
 12. The processof claim 10 wherein the anode and the substrate on which the anode isformed are transparent to the light emitted by the light emittingmaterial.
 13. The process of claim 8 wherein the mold is made of anelastomeric material.
 14. The process of claim 10 wherein the patternedactive material is a light-emitting material that is soluble in anorganic solvent and wherein the process further comprises wetting themold surface having the recessed portion with an organic solvent priorto contact between the mold surface and the light-emitting material.